Many systems and tools have been developed for supporting workpieces while they are being machined. These systems and tools have the common objective of holding the workpiece with sufficient accuracy that the machining satisfies the tolerance requirements for the particular part. The closer the tolerances, the greater the necessity for accurate positioning of the workpiece and the greater the necessity that the workpiece be held against deflection resulting from tool pressure. One approach to this problem has been the use of a jig on which the part is mounted. A jig support is provided at the tool to hold and locate the jig with respect to the tool. In many cases the jig with the workpiece secured to it is moved from machine to machine so that various machining operations can be performed on the workpiece. In many cases the jigs are expensive and their usefulness is limited to a part of a single design and size. Once the production run of the workpiece is finished, the jig has no further utility and is scrap. An example of this type of jig is disclosed in U.S. Pat. 2,176,089 issued Oct. 17, 1939 to F. J. Malone. The cost of this type of tooling coupled with its one-part utility limits the use of this type of tooling to parts requiring mass production.
An even more costly and specialized approach to the problem of holding workpieces for machining is disclosed in U.S. Pat. No. 2,392,169 issued Jan. 1, 1946, to J. H. Mansfield and U.S. Pat. No. 4,309,600 issued Jan. 5, 1982, to C. B. Perry et al. These involve the design of entire systems for multiple machining of parts. To change over systems of this type from one part design to another necessitates a long and costly rebuilding procedure. Thus, the system is useful only for mass produced products having long production runs whereby the cost of the system can be amortized.
Even with the investment in the foregoing systems, the problem of tolerance control remains. The systems are basically incapable of dependably controlling tolerances to less than 0.005 inches.
For the purpose of machining parts when only small quantities are needed, various types of workpiece holders have been developed. An example of this type of workpiece holder is disclosed in U.S. Pat. No. 4,184,669, issued Jan. 22, 1980, to H. Bald. While this type of workpiece holder can be adapted to mount parts of various designs, accurately positioning each workpiece is time consuming and requires both skill and experience. Thus, it is expensive to use. Further, it does not solve the problem of tolerance control.
In many cases, a chuck or collet could be used as the workpiece support. This would significantly improve tolerance control. However, chucks and collets have a very limited range of adjustment for workpieces of different sizes, normally only a few tenths of an inch. Thus, the change over from one part to another involves replacing the chuck or collect to adapt the machine from one workpiece to another. This is a time consuming operation. Further, each time such a change is made the replacement chuck or collet, has to be checked for accuracy of mounting including concentricity with the tool itself. Normally, it also has to be checked for axial position. This is true whether the chuck is mounted for stationary or driven use. The result again is a time consuming and expensive operation. It is also an important cost factor that while the chucks or collets are being exchanged and the replacement checked for accuracy, the machine on which mounting is done is out of production. These machines involve a very substantial capital investment. Therefore, their downtime is costly. This materially adds to the cost of the operation and has a material negative effect upon productivity.